The present invention relates to improvement of a parking lock system for a vehicle having an automatic transmission.
When a vehicle with an automatic transmission is parked on a slope, it is necessary to lock the output shaft of the transmission because the transmission has been disengaged from the output shaft of an engine.
In order to lock the output shaft of the transmission, a parking gear is provided on the output shaft of the automatic transmission, and is put into engagement with a parking pawl to lock the shaft during parking, so that rotation of the output shaft is prevented. Japanese Patent Laid-open No. 55-164527 has already disclosed such a construction comprising a parking gear and a parking pawl engaged with each other by means of a cam provided on a parking rod during parking of a vehicle, and disengaged while the vehicle is being driven using a return spring to retract the cam to release the pawl from the gear.
The conventional parking lock mechanism is usually assembled by attaching a cover, which contains a lock system comprising a parking pawl, a return spring, and other parts, to the transmission case. However, the assembling of the cover to the transmission case, with each part in its position on the inside of the cover is difficult, because the return spring always biases the parking pawl out of position. A conventional parking lock mechanism is shown in FIGS. 3 to 5.
As shown in FIGS. 3 to 5, an automatic transmission case 1 is provided with a cover 2 thereon which covers a parking gear 4 mounted on an output shaft 4a at an open side of the case 1. A shaft 6 bridges the space between the case 1 and the cover 2 and pivotally supports a parking pawl 3. When the vehicle is parked, a parking rod 7 is shifted from the position shown by the chain line to the solid line position, bringing a parking cam 7a secured to the rod 7 between a support plate 10 and the pawl 3 so that the pawl 3 is rotated by the cam 7a to engage with the gear 4, arresting the rotation of the output shaft 4a of the transmission. When starting of the vehicle, the parking cam 7a is retracted from the pawl 3 to remove it from the gear 4 by means of the force of a return spring 5. This spring 5 is engaged at one end on a projection 1c of the case 1, and at the other end on a side face of the parking pawl 3, and biases the pawl 3 away from the gear 4.
In this construction, it takes a long time to assemble the parking lock system because the shaft 6 tends to fall and come out of place by the force of the spring, and hence the parking pawl 3 must be held in place against the action of the spring 5.